This is old, but I'll add some info since I use these bags.
They have two coated metal hooks on the top, and a hook on the bottom that's tightened with a buckle. I use a cheap blackburn rack, and everything works ok. I had to shorten the strap for the lower hook just a bit so I could get it was a little more snug.
They definitely help with heel clearance, but their odd shape can be a pain.
I think they're a good value, they work fine, and have a built in rain fly.